Before the introduction of monkey, the word for a monkey, and afterwards still sometimes so used, especially in poetic and literary sources, and when the animal is taken as typifying the ability to imitate human behaviour, especially in an absurd or unthinking way.
an ape's an ape, a varlet's a varlet, though they be clad in silk or scarlet whatever the outward show, the essential quality of a person or thing remains unchanged. A varlet was formerly a menial servant, but the word took on the sense of ‘scoundrel’ or ‘rogue’. Scarlet was the colour of the official or ceremonial dress of various dignitaries, including judges. The saying is recorded in English from the mid 16th century, although the Greek writer Lucian, of the 2nd century ad, has ‘an ape is an ape…even if it has gold insignia.’
See also naked ape.